Such a flexible pipe is for example made according to normative documents API 17J (Specification for Unbonded Flexible Pipe) and API RP 17B (Recommended Practice for Flexible Pipe) established by the American Petroleum Institute.
The pipe is generally formed by a set of concentric and superimposed layers. It is considered “unbonded” within the meaning of the present invention when at least one of the layers of the pipe is able to move longitudinally relative to the adjacent layers when the pipe is bent.
In particular, an unbonded pipe is a pipe with no bonding materials connecting the layers forming the pipe.
In a known manner, such a pipe includes a tubular inner structure comprising at least one pressure sheath. The pipe includes plies of tensile armours positioned around the inner tubular structure.
In some cases, the pipe further includes a pressure vault, formed by at least one interlocked wire having a T-shaped profile or a Z-shaped profile. A hoop layer can also be wound in a spiral around the pressure vault.
One example pipe of the aforementioned type is described in WO 2011/026801. This pipe further includes a protection fluid received between the inner sheath and the outer sheath. The protection fluid prevents corrosion of the layers of intermediate armours. It is kept at atmospheric pressure.
The ducts of the aforementioned type generally positioned through an expanse of water, between a bottom assembly, designed to collect the fluid mined in the bottom of the expanse of water, and a floating or non-floating surface assembly designed to connect and distribute the fluid. The surface assembly may be a semisubmersible platform, an FPSO, a stationary platform, a flexible tower, a tension leg platform or any other floating or non-floating assembly.
In some cases, the pipe is used to reinject, into the bottom of the expanse of water, a fluid present on the surface, for example a pressurized gas. This is in particular the case for deposits comprising carbon dioxide-rich hydrocarbons. The carbon dioxide is separated from the surface hydrocarbons and is reinjected into the reservoir under pressure, in order to avoid the dissemination of carbon dioxide into the atmosphere.
In some cases, for the exploitation of fluids in deep water, the flexible pipe has a length exceeding 200 m. Furthermore, the differential pressure necessary for the reinjection of fluid into the reservoir can be very high, for example above 400 bars, or even above 700 bars. Furthermore, the absolute pressure reigning in the bottom of the flexible pipe, which is a combination of very high fluid pressure at the top of the pipe and the exerted hydrostatic pressure, can be very high, for example approximately 1300 bars.
When the fluids are conveyed at very high pressures, the ducts with a traditional construction of the aforementioned type can be limited, particularly for use in a dynamic application.
Indeed, fatigue phenomena, and more particularly fatigue-fretting phenomena, may appear on the pressure vault and the spiral hoop layer.
This fatigue alters the mechanical properties of the pipe and harms longevity. One aim of the invention is therefore have a flexible pipe for transporting a fluid, able to convey a fluid at a very high pressure and that is nevertheless very strong over time for dynamic applications.